The United States population will expand by 100 million over the next 40 years. Is this a reason to worry?

Estimates of the United states population at the middle of the 21st century vary, from the U.N.’s 404 million to the U.S. Census Bureau’s 422 to 458 million. To develop a snapshot of the nation at 2050, particularly its astonishing diversity and youthfulness, I use the nice round number of 400 million people, or roughly 100 million more than we have today.

Though cost of living in "superstar cities" (here, New York’s Times Square) will drive the middle class to the suburbs, there will be 15 to 20 million more urban dwellers by 2050
(Patrick Zachmann / Magnum Photos)

According to a recent study, neighborliness in the suburbs (here, a Las Vegas-area development) is more pronounced than expected.
(Cameron Davidson / Aerialstock)

Businesses such as this wind farm near Milford, Utah, as well as families, are shifting from urban centers to metropolitan-area suburbs.
(Cameron Davidson / Courtesy of Clipper Windpower)

The nation will be more diverse, with today's minorities making up more than half of the total population.
(Graphics by Linda Eckstein and Samuel Velasco for 5W Infographics)

A smaller percentage of workers will be supporting a larger number of elderly.
(Graphics by Linda Eckstein and Samuel Velasco for 5W Infographics)

New immigrants and their U.S.-born descendants will account for more U.S. population growth. Predicting future illegal immigration is difficult.
(Graphics by Linda Eckstein and Samuel Velasco for 5W Infographics)

Average Annual Migration 2010-2050, in Thousands
(Graphics by Linda Eckstein and Samuel Velasco for 5W Infographics)

In 2050, median age will range from early 20s to mid 50s, with the worldwide median age being 38.4 years.
(Graphics by Linda Eckstein and Samuel Velasco for 5W Infographics)

Average life expectancy of the top three longest-living populations will increase by 4.6 years, while that of the shortest-living populations will increase by 13.5 years, or 30 percent.
(Graphics by Linda Eckstein and Samuel Velasco for 5W Infographics)

Most populous countries
(Graphics by Linda Eckstein and Samuel Velasco for 5W Infographics)

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The United States is also expected to grow somewhat older. The portion of the population that is currently at least 65 years old—13 percent—is expected to reach about 20 percent by 2050. This “graying of America” has helped convince some commentators of the nation’s declining eminence. For example, an essay by international relations expert Parag Khanna envisions a “shrunken America” lucky to eke out a meager existence between a “triumphant China” and a “retooled Europe.” Morris Berman, a cultural historian, says America “is running on empty.”

But even as the baby boomers age, the population of working and young people is also expected to keep rising, in contrast to most other advanced nations. America’s relatively high fertility rate—the number of children a woman is expected to have in her lifetime—hit 2.1 in 2006, with 4.3 million total births, the highest levels in 45 years, thanks largely to recent immigrants, who tend to have more children than residents whose families have been in the United States for several generations. Moreover, the nation is on the verge of a baby boomlet, when the children of the original boomers have children of their own.

Between 2000 and 2050, census data suggest, the U.S. 15-to-64 age group is expected to grow 42 percent. In contrast, because of falling fertility rates, the number of young and working-age people is expected to decline elsewhere: by 10 percent in China, 25 percent in Europe, 30 percent in South Korea and more than 40 percent in Japan.

Within the next four decades most of the developed countries in Europe and East Asia will become veritable old-age homes: a third or more of their populations will be over 65. By then, the United States is likely to have more than 350 million people under 65.

The prospect of an additional 100 million Americans by 2050 worries some environmentalists. A few have joined traditionally conservative xenophobes and anti-immigration activists in calling for a national policy to slow population growth by severely limiting immigration. The U.S. fertility rate—50 percent higher than that of Russia, Germany and Japan and well above that of China, Italy, Singapore, South Korea and virtually all the rest of Europe—has also prompted criticism.

Colleen Heenan, a feminist author and environmental activist, says Americans who favor larger families are not taking responsibility for “their detrimental contribution” to population growth and “resource shortages.” Similarly, Peter Kareiva, the chief scientist at the Nature Conservancy, compared different conservation measures and concluded that not having a child is the most effective way of reducing carbon emissions and becoming an “eco hero.”

Such critiques don’t seem to take into account that a falling population and a dearth of young people may pose a greater threat to the nation’s well-being than population growth. A rapidly declining population could create a society that doesn’t have the work force to support the elderly and, overall, is less concerned with the nation’s long-term future.